This invention relates to a torque control method for a vehicle engine, and more particularly to a control method for suppressing a detected power-hop condition while minimizing degradation of vehicle acceleration.
Vehicles equipped with high torque engines, aggressive tires and lightweight driveline components can experience an undesired condition referred to as power-hop during a high torque vehicle launch. In general, power-hop is a condition of driveline instability initiated when the tractive effort decreases due to tire slip beyond an optimal slip value. If the engine torque is sufficiently high, the power-hop condition can be sustained, resulting in both torsional oscillation of the vehicle driveline and vertical oscillation of suspension members. Various techniques for suppressing power-hop include increasing driveshaft and half-shaft stiffness, decreasing tire aggressiveness, and equipping the driveline with dampers or auxiliary flywheels. However, each of these techniques increases cost and/or decreases performance. Accordingly, what is needed is a technique that effectively suppresses power-hop with minimal impact on vehicle cost and performance.
The present invention is directed to an improved engine torque control method that uses existing vehicle sensors and controls to reliably detect and suppress power-hop with minimum degradation of vehicle acceleration. Power-hop is detected by identifying a characteristic oscillation (magnitude and frequency) of the driven wheels. Once a power-hop condition is detected, the control method computes a desired engine torque output for suppressing the detected power-hop without unnecessarily degrading vehicle performance, based on the wheel oscillation magnitude, the engine speed and vehicle acceleration. A combination of engine cylinder fuel cut-off and spark retard is then scheduled for reducing the engine output torque to the desired level for the duration of the power-hop condition. The control method has minimal impact on vehicle cost since it is performed (preferably) by engine or other control software, and has been shown to quickly and effectively suppresses power-hop and its disadvantages without significantly degrading vehicle performance.